Radioactive waste is obviously a serious matter, but it's hard not to think of George R.R. Martin and the Wall built across the northern border of the Seven Kingdoms to keep out the Others. In fact, this reminds me of a worry I've long had about long-term storage of nuclear waste. The issue is that it's very difficult to credibly signal the presence of something dangerous over a long period of time. Egyptian tombs were inscribed with many warnings about the curses that would befall grave robbers, but later generations of thiefs and archeologists simply dismissed those warnings as myths. And conveniently for us, they are just myths. In Martin's story, though, generations of peace leave people believing that stories about the Others are just myths leading them to leave the defensive structures under-manned and under-serviced but they're not myths. I have at least some doubts that you could effectively label any kind of containment system in a way that would be consistently believed. Radiation is almost too weird of a concept—"if you open this barrier tiny invisible particles will give you cancer" sounds an awful lot like a curse.